No picture, changed logic board

Hello I have this imac model (a1224) which has ati radeon 2600hd. I used to have no picture just power on (diagnostic leds only the first was ON). I changed the logic board now I have 3 out of 4 leds ON but no picture even on VGA out and also now I have the chime. I think that the problem might be from the VGA board. After changing the logic board is there any necessary adjustment that needs to be done or it will just work?